Structural Investigations of Ammonium Vanadium Diphosphates by X-Ray Powder Diffraction

✍ Scribed by J. Trommer; H. Worzala; S. Rabe; M. Schneider

• Publisher: Elsevier Science
• Year: 1998
• Tongue: English
• Weight: 586 KB
• Volume: 136
• Category: Article
• ISSN: 0022-4596
• DOI: 10.1006/jssc.1997.7673

✦ Synopsis

The crystal structures of three ammonium vanadium diphosphates have been investigated by means of X-ray powder diffraction including ab initio structure determination and Rietveld refinement. The compound NH 4 VP 2 O 7 crystallizes in the monoclinic space group P2 1 /c with a ‫؍‬ 7.5149(2) A s , b ‫؍‬ 10.0384(3) A s , c ‫؍‬ 8.2422(2) A s , ‫؍‬ 105.988 (3)°, and Z ‫؍‬ 4. The two ammonium vanadyl diphosphates are (NH 4 ) 2 VOP 2 O 7 , which has a tetragonal unit cell, space group P4bm, a ‫؍‬ 8.3039(2) A s , c ‫؍‬ 5.7658(2) A s , and Z ‫؍‬ 2, and -(NH 4 ) 2 (VO) 3 (P 2 O 7 ) 2 , which has an orthorhombic structure, space group Pnam, a ‫؍‬ 17.4973(4) A s , b ‫؍‬ 11.3655(3) A s , c ‫؍‬ 7.2769(2) A s , and Z ‫؍‬ 4. The first and the third structures consist of a framework of corner-sharing VO x polyhedra and PO 4 tetrahedra and intersecting channels, whereas (NH 4 ) 2 VOP 2 O 7 is arranged in layers built-up from VO 5 square pyramids and P 2 O 7 groups and the NH ؉ 4 cations in between. The three NH 4 compounds are isostructural to the equivalent alkali vanadium diphosphates.